US20080188883A1 - Lancet device - Google Patents

Abstract

The present invention relates to a lancet device, by which a lancet can be displaced along a piercing path for generating a piercing wound in a skin surface, in particular to obtain bodily fluid for diagnostic purposes, comprising a lancet drive having drive means to generate a drive force for a piercing movement of the lancet along the piercing path in the direction toward the skin surface. According to the present invention, the lancet drive comprises a magnet, by which a magnetic retention force oriented opposite to the drive force may be generated, and the lancet drive also comprises triggering means, by which the retention force may be reduced enough that the lancet is accelerated in the direction toward the skin surface under the effect of the drive force generated by the drive means. The present invention also relates to a method for generating a piercing wound, in which the drive spring is held in a tensioned state using a magnetic retention force oriented opposite to the drive force before the triggering of a piercing wound.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application is a continuation of International Patent Application No. PCT/EP2006/005929 filed Jun. 21, 2006, which claims the benefit of European Patent Application No. 06 004 319.7 filed Mar. 3, 2006 and of European Patent Application No. 05 015 171.1 filed Jul. 13, 2005, which are all hereby incorporated by reference in their entirety.
BACKGROUND
• The present invention relates to a lancet device, by which a lancet can be displaced along a piercing path to generate a piercing wound in a skin surface, in particular to obtain bodily fluid for diagnostic purposes, comprising a lancet drive having drive means for generating a drive force for a piercing movement of the lancet along the piercing path in the direction toward the skin surface.
• Furthermore, the present invention relates to a method for generating a piercing wound in a skin surface using a lancet, in which the lancet is accelerated along a piercing path using a drive force generated by a drive spring in the direction toward the skin surface.
• Lancet devices are required, for example, by diabetics, who have to check their blood sugar level frequently to be able to keep it within specific setpoint limits by insulin injections. Extensive scientific experimentation has proven that a dramatic reduction of the most severe long-term complications of diabetes mellitus (such as retinopathy with resulting blinding of the patient) may be achieved using an intensive treatment having at least four analyses per day.
• For users of lancet devices, on one hand the most low-pain piercing possible and on the other hand the simplest possible operation and ability to handle the lancet device used are of great significance.
• A requirement for low-pain piercing is the most rapid possible piercing movement having a short dwell time of the lancet in the skin. The use of drive springs has proven itself in the prior art for a correspondingly strong acceleration of the lancets. A disadvantage of lancet devices of this type is that manually tensioning the drive springs after completed piercing is cumbersome for many users. This is true in particular for people whose manual dexterity is restricted by age or illness.
• A lancet device in which the drive spring is automatically tensioned by an electric motor does offer increased user comfort in this regard, but has the disadvantage of being larger and heavier because of the electric motor. A lancet device having an integrated electric motor therefore represents a burden for the user, who has to carry it around continuously for frequent measurements. In addition, the production costs are significantly increased by an electric motor.
• Furthermore, lancet devices are known in the prior art in which the drive force is generated electromagnetically using a coil. Lancet devices of this type are disclosed, for example, in WO 02/100460 A2 and U.S. Pat. No. 6,364,889 B1. To be able to cause a sufficiently rapid piercing movement for a low-pain piercing using electromagnetic lancet drives of this type, strong magnetic fields must be generated. This requires that relatively strong electric currents flow through the drive coils used, which may be generated not at all or only with great effort in a small, compact handheld device. Electromagnetic lancet drives have therefore not been able to succeed against mechanical drives having drive springs up to this point.
SUMMARY
• The object of the present invention is to show a cost-effective way in which, in a lancet device of the type cited at the beginning, having a compact design, a sufficiently rapid piercing movement for a low-pain piercing may be generated and the user may be relieved as much as possible from preparatory handling, such as tensioning a drive spring.
• This object is achieved according to the present invention using a lancet device of the type cited at the beginning in that the lancet drive comprises a magnet, by which a magnetic retention force oriented opposite to the drive force may be generated, and the lancet drive also comprises trigger means, by which the retention force may be reduced enough that the lancet is accelerated in the direction toward the skin surface under the effect of the drive force generated by the drive means.
• A drive spring may be used as the drive means, which may be held in a tensioned state by the magnetic retention force. In a lancet device according to the present invention, the lancet may be retracted into its starting position via the magnetic retention force after the penetration into the skin surface. The retention force may be generated using an electromagnetic, for example, or—preferably—originate from a permanent magnet. If a permanent magnet is used, it is advantageous if the trigger means comprise a coil, by which a magnetic field may be generated, which at least partially, preferably completely compensates for the retention force of the permanent magnet. Through suitable dimensioning of the permanent magnet and the coil, the retention force generated by the magnet may be sufficiently great to cause renewed tensioning of the drive spring after completed piercing.
• A lancet device according to the present invention having a drive spring has the advantage that it may be manufactured significantly more cost-effectively and compact than a lancet device having an electric motor, and nonetheless allows automatic tensioning of the drive spring.
• Furthermore, a coil may be used as the drive means for a lancet device according to the present invention, to generate the drive force magnetically. The coil may also be used as the triggering means, using which the magnetic retention force is overcompensated for. The magnetic retention force is preferably generated by a permanent magnet, to which a further permanent magnet is assigned as the second part of the drive means as a drive magnet having reversed polarization, so that the magnetic fields of the permanent magnets are destructively superimposed. In this way, the drive force generated by the drive magnet is compensated for by the permanent magnet generating the retention force, so that no resulting drive force and therefore also no lancet movement results without coil current. If a current flows through the drive coil, the magnetic field of the drive magnet is superimposed constructively on the magnetic field of the coil, so that a resulting drive force to accelerate a lancet arises.
• Even if the two permanent magnets compensate for one another exactly, a greater drive force may surprisingly be generated by the use of a drive coil in combination with oppositely polarized permanent magnets than using a drive coil alone. By superimposing the coil field with the fields of the oppositely polarized permanent magnets, an increased magnetic field strength results locally in a first area and a locally reduced field strength results in a second area. The locally increased magnetic field strength may be used for the purpose of magnetizing a drive element, such as a soft-magnetic coil core. The force exerted by the magnetic field on the drive element is overall greater because of the locally increased field strength than if a coil is used without permanent magnets. An important aspect of the present invention, which may also be significant independently, therefore relates to a lancet device comprising a lancet drive having:
• • a first and a second magnetic field source, which generate two magnetic fields destructively superimposed in a drive chamber in operation,
  • a third magnetic field source, which generates a further magnetic field in operation, which is superimposed constructively with the magnetic field of the first magnetic field source and destructively with the magnetic field of the second magnetic field source in the drive chamber, at least one of the three magnetic field sources being a permanent magnet and at least one of the three magnetic field sources being a coil, and
  • a drive element in the form of a soft-magnetic coil core, which is movable back and forth between a first position and a second position in the drive chamber, to cause a piercing and retraction movement by coupling with a lancet, the magnetization of the coil core being determined by the third magnetic field source, so that the coil core is movable by a coil current from the first position into the second position and is movable back into the first position by reversing the direction of the coil current.
• The object of the present invention is also achieved by a method of the type cited at the beginning according to the present invention in that the drive spring is held in a tensioned state before the triggering of a piercing movement using a magnetic retention force oriented opposite to the drive force, and the retention force is reduced enough to trigger a piercing movement that the drive spring relaxes and the lancet is accelerated in the direction toward the skin surface under the effect of the drive force generated by the drive spring.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention is explained in greater detail in the following on the basis of exemplary embodiments illustrated in the figures. The special features illustrated therein may be used individually or in combination to provide preferred designs of the present invention.
• FIG. 1 shows an exemplary embodiment of a lancet device according to the present invention having tensioned drive spring;
• FIG. 2 shows the exemplary embodiment shown inFIG. 1 having relaxed drive spring;
• FIG. 3 shows the exemplary embodiment shown in a further illustration;
• FIG. 4 shows a further exemplary embodiment of a lancet drive of a lancet device according to the present invention in a diagonal view in partial section;
• FIG. 5 shows the field course of the magnetic fields generated by the permanent magnets of the lancet drive shown inFIG. 4;
• FIG. 6 shows the field course of the magnetic field generated in operation by the coil windings of the lancet drive shown inFIG. 4, and
• FIG. 7 shows the course of the overall field which results by superposition of the magnetic field shown inFIGS. 5 and 6.
DETAILED DESCRIPTION OF SELECTED EMBODIMENTS
• The lancet device illustrated inFIGS. 1 through 3 may be integrated in a handheld analysis device, for example, which has a measuring apparatus for assaying bodily fluid, which is obtained from a generated piercing wound. The lancet device may also be installed in a separate device as a puncture aid.
• The central component of thelancet device1 shown is alancet drive2, which comprises apushrod3, drive means in the form of adrive spring4, acoil6, and apermanent magnet5 situated axially in thecoil6. Thepushrod3 carries alancet holder7 having areplaceable lancet8 and is accelerated along a piercing path predefined by theguide10 using thedrive spring4, which is implemented as a coiled spring, to generate a piercing wound.
• Thepushrod3 is shown in its rest position having tensioneddrive spring4 inFIG. 1. Thepushrod3 is held in this position by the magnetic retention force of thepermanent magnet5 integrated in thecoil core11 of thecoil6. Thecoil core11 having thepermanent magnet5 is situated fixed in relation to thecoil6. Thecoil6 is used as the triggering means for triggering a piercing movement. A magnetic field is generated by causing an electric current to flow through thecoil6, which compensates for the retention force of thepermanent magnet5, so that thedrive spring4 relaxes and thepushrod3 having thelancet8 is accelerated in the direction toward the skin surface under the effect of the drive force thus generated by thedrive spring4.
• Thepushrod3 is preferably made of plastic and carries anarmature plate12 made of iron or another ferromagnetic material, using which a magnetic circuit, which contains thepermanent magnet5 and apole shoe16 enclosing thecoil6, is closed in the position shown inFIG. 1.
• Thearmature plate12 may also be implemented as a permanent magnet, so that it may not only be attracted by thepermanent magnet5, but rather may also be repelled and additionally accelerated by a magnetic field generated by the coil.
• A comparison ofFIGS. 1 and 2 shows that thepushrod3 has a section projecting into thecoil core11 in the rest position. Improved guiding is achieved in this way.
• FIG. 2 shows thelancet device1 having thepushrod3 in the piercing position. In the piercing position, a stop formed by thearmature plate12 presses against adelimitation element13 of theguide10, so that the piercing path is delimited.
• In addition to thedrive spring6, thelancet drive2 also comprises a restoringspring14 for generating a retraction movement of thelancet8. Thedrive spring4 is tensioned again by the retraction movement. Drivespring4 and restoringspring14 are each implemented as coiled springs which enclose thepushrod3. Thedrive spring4 and the restoringspring14 are each supported at one end on asupport section15 of thepushrod3, which is implemented as a thickened part in the exemplary embodiment shown, and at the particular other end on theguide10. Thedrive spring4 and the restoringspring14 are situated in such a way that relaxation of thedrive spring4 causes tensioning of the restoringspring14 and relaxation of the restoringspring14 causes tensioning of thedrive spring4.
• The term “tensioning” is to be understood in this context to mean that energy is stored in the particular effective spring. This may be caused by compression in a compression spring and by stretching in an expansion spring.
• Of course, friction forces occur in thelancet device1 shown, so that the energy stored in the restoringspring14 in the piercing position shown inFIG. 2 is not entirely sufficient for tensioning thedrive spring4 again. In the illustrated device, the restoringspring14 is therefore supported by thepermanent magnet5 during the retraction movement of thepushrod3. The retention force generated by thepermanent magnet5 and the spring force provided by the restoringspring14 are sufficient with an appropriate design of thepermanent magnet5 to bring thepushrod3 back into the rest position shown inFIG. 1 and tension thedrive spring4. By suitable shaping of the ends of thepole shoe16, for example, by beveling the ends, the force-distance characteristic of the retention force generated by the permanent magnet may be influenced and the retraction movement may additionally be supported.
• In order that the retention force of thepermanent magnet5 may be used for tensioning thedrive spring4 again, it is sufficient to turn off the current which is sent through thecoil6 to trigger a piercing. As soon as current no longer flows through thecoil6, a magnetic field is also no longer generated by thecoil6, so that the retention force of thepermanent magnet5 is no longer compensated for and is added to the spring force of the restoringspring14.
• A piercing and retraction movement of the lancet typically lasts a total of 4 ms to 6 ms. In order that the retention force of the permanent magnet may be used for tensioning the drive spring again, the current which is sent through thecoil6 to trigger a piercing is therefore preferably turned off after 1 ms to 3 ms, preferably 1.5 ms to 2.5 ms. A current pulse having the steepest possible flanks, ideally having a rectangular profile, is especially well suitable.
• An appropriatelystrong drive spring4 and an appropriately strongpermanent magnet5, such as a rare earth magnet, are preferable for the most rapid possible piercing movement. To compensate for the magnetic retention force, voltages and/or current strengths which greatly exceed the performance capability of commercially available batteries are therefore preferably used. Thecoil6 is therefore preferably connected via a current buffer and/or a voltage converter to an internal current source of the lancet device, such as a battery, so that a current pulse capable of compensating for the magnetic retention force may be generated using commercially available batteries. For example, capacitors or accumulators, in particular lithium-polymer accumulators, are suitable as the current buffer. Suitable voltage converters are available as DC/DC converters. The corresponding technology for generating intensive current pulses is typical in photographic apparatus for generating light flashes, for example, and may be used for the described lancet device.
• To additionally support the retraction movement, the direction of the current flowing through thecoil6 to trigger a piercing may be reversed in polarity, so that the magnetic field generated by thecoil6 is added to the retention force of thepermanent magnet5. For example, a control unit having an H bridge may be used for reversing the polarity of the current. Ideally, the polarity is reversed at the moment in which the lancet has reached the outermost point of the piercing path.
• A further possibility for moving thepushrod3 from an intermediate position shown inFIG. 3 back into the rest position in case of malfunction is to excite a mechanical oscillation of the mechanical system formed by thedrive spring4, the restoringspring14, and thepushrod3 by periodic current surges. Upon continued excitation at the resonance frequency of this system, the amplitudes of this oscillation increase until thepushrod3 returns into the rest position and may be held there by the retention force of thepermanent magnet5.
• It may be established by a measurement of the inductance of thecoil6 whether thearmature plate12 presses against thepole shoe16. In this way, it may thus be ascertained whether or not thepushrod3 is located in the rest position shown inFIG. 1. The inductance of thecoil6 is preferably measured shortly after a piercing, for example, 1 to 2 seconds after a piercing. If it is established that thepushrod3 is not located in the rest position, a mechanical oscillation of the mechanical system formed by thedrive spring4, the restoringspring14, and thepushrod3 is excited by periodic current surges, so that thepushrod3 returns into its rest position.
• In this way, thecoil6 is used as a position sensor for the position of thepushrod3. The illustrated lancet device may alternatively or additionally also be equipped with other position sensors, so that the optimal instant for turning off or reversing the polarity of the current through thecoil6 may be ascertained as a function of the instantaneous position of thepushrod3. The use of sensors therefore allows, instead of simple control of the coil current, in which a predefined profile is predefined for a current pulse, regulation of the coil current as a function of the position of thepushrod3.
• A further exemplary embodiment of alancet drive2 for a lancet device is shown inFIG. 4. In the exemplary embodiment shown inFIG. 4, acoil20 is used as the drive means for generating the drive force, which encloses adrive chamber21, in which a drive element in the form of a soft-magnetic coil core22 is movable back and forth to cause a piercing and retraction movement of the lancet by coupling to a lancet, for example, using apushrod3 shown inFIGS. 1 through 3. Thedrive chamber21 is also enclosed bypermanent magnets23,24, which are implemented as magnet rings in the exemplary embodiment shown. The permanent magnet rings23,24 are ideally situated concentrically to thecoil20.
• As the field course of the magnetic field generated by thepermanent magnets23,24 illustrated inFIG. 5 shows, thepermanent magnets23,24 are situated with opposite polarity. Thepermanent magnets23,24 thus represent a first and a second magnetic field source, which generate two magnetic fields destructively superimposed in thedrive chamber21. Ideally, the twopermanent magnets23,24 are identical and are only situated differently. Thepermanent magnets23,24 preferably differ in their strength by less than 30%, especially preferably by less than 20%, particularly by less than 10%.
• Thepermanent magnets23,24 work together with thecoil20, which generates a further magnetic field as the third magnetic field source in operation, whose field course is shown inFIG. 6. To trigger a piercing, electric current is caused to flow through the windings of thecoil20, so that the overall magnetic field shown inFIG. 7 results. As may be seen therein, the magnetic field generated by the coil is superimposed constructively in thedrive chamber21 on the magnetic field of thepermanent magnet24 and destructively on the magnetic field of thepermanent magnet23. In this way, an overall field results in thedrive chamber21 which is extensively reduced, ideally canceled out in a firstpartial area31 by destructive superposition, and is reinforced, ideally doubled, in a secondpartial area32. The twopartial areas31,32 are ideally equally large.
• Before the coil current is turned on, the magnetization direction of thecoil core22 is determined by thepermanent magnet23, so that thecoil core22 is drawn into the firstpartial area31 of thedrive chamber21 by thepermanent magnet23, but pushed out of the secondpartial area32 of thedrive chamber21 by the oppositely polarizedpermanent magnet24. Therefore, the position of thecoil core22 shown inFIG. 5 results before a coil current is turned on.
• An increased overall field results in the secondpartial area32 of thedrive chamber21 by turning on the coil current, which causes a reversal of the magnetization of the soft-magnetic coil core22. As a result of this reversal of the magnetization direction of thecoil core22, thecoil core22 is drawn into the secondpartial area32 of thedrive chamber21 and thus moved out of the position shown inFIG. 5 into a second position. The stroke of thecoil core22 connected thereto may be used for a piercing movement.
• The relationships of the overall field course shown inFIG. 7 may be reversed by a reversal of the direction of the current through thecoil20, so that an increased overall field results in the firstpartial area31 of thedrive chamber21 by constructive superposition and a reduced overall field results in the secondpartial area32 of thedrive chamber21 by destructive superposition. A change of the overall field of this type causes another change of the magnetization direction of thecoil core22, so that the coil core is retracted into the firstpartial area31 of thedrive chamber21 and again reaches the first position.
• The length of thecoil core22 is less than the length of thedrive chamber21 enclosed by the first and the second magnetic field sources, i.e., thepermanent magnets23,24, preferably at least 10% shorter. In this context, only the length of a soft-magnetic part is to be understood as thecoil core22. Possible parts which are attached to a soft-magnetic part, but are not magnetic themselves, such as a pushrod made of plastic, are not to be viewed as the coil core in this regard.
• The drive principle described on the basis ofFIGS. 4 through 7 may also be used in a corresponding way in that the twopermanent magnets23,24 are replaced by coils having opposing winding directions and thecoil20 is replaced by a permanent magnet of suitable strength.
• In the exemplary embodiment shown inFIG. 4, thecoil core22 is situated in a slidingtube25. The slidingtube25 is centered using centeringrings26 in thedrive chamber21 inside the soft-magnetic return path28, which is formed by an iron tube which encloses thepole shoe27, thepermanent magnets23,24, and also thecoil20 and thedrive chamber21. Soft-magnetic pole shoes27 are placed on the slidingtube25 and thepermanent magnets23 and24 are placed having opposite polarization direction between the pole shoes27.
• In the exemplary embodiment described on the basis ofFIGS. 4 through 7, thepermanent magnet23 generates a magnetic retention force which is oriented opposite to the drive force generated by thepermanent magnet24 and thecoil20. Thecoil20 is both triggering means and also drive means in this exemplary embodiment. Using thecoil20 as the triggering means, the retention force generated by thepermanent magnet23, namely its magnetic field, may be reduced enough that thelancet8 is accelerated in the direction toward the skin surface under the effect of the drive force generated by the drive means, namely thepermanent magnet24 and thecoil20.
• As in the exemplary embodiment described on the basis ofFIGS. 1 through 3, in the exemplary embodiment described on the basis ofFIGS. 4 through 7, thecoil20 is also connected via a current buffer and/or a voltage converter to an internal current source of the lancet device, such as a battery, so that an intensive current pulse may be generated using commercially available batteries. For the most rapid possible piercing and retraction movement, it is favorable to perform changes of the voltage applied to thecoil20 as rapidly as possible, i.e., to use voltage pulses having a rectangular voltage profile. The voltage supply of thecoil20 therefore delivers voltage pulses having rectangular flanks. Rectangular voltages are especially favorable, because the retraction movement of the lancet may be initiated by the voltage change of a rectangular voltage pulse.

Claims (17)

1. A lancet device, by which a lancet can be displaced along a piercing path to generate a piercing wound in a skin surface, in particular to obtain bodily fluid for diagnostic purposes, comprising

a lancet drive having drive means for generating a drive force for a piercing movement of the lancet along the piercing path in the direction toward the skin surface,

the lancet drive comprises a magnet, by which a magnetic retention force directed opposite to the drive force may be generated, and

the lancet drive also comprises triggering means, by which the retention force may be reduced enough that the lancet is accelerated in the direction toward the skin surface under the effect of the drive force generated by the drive means,

the drive means comprises a further permanent magnet which is situated with opposite polarity to the permanent magnet generating the retention force.

2. The lancet device according toclaim 1, wherein the drive means comprises a drive spring, wherein the drive spring can be held in a tensioned state by the magnetic retention force.

3. The lancet device according toclaim 2, wherein the drive spring is a coiled spring, which encloses a pushrod, which carries the lancet.

4. The lancet device according toclaim 2, wherein the lancet drive comprises a restoring spring to generate a retraction movement of the lancet, during which the drive spring is tensioned again.

5. The lancet deviceclaim 1, wherein the magnet is a permanent magnet.

6. The lancet device according toclaim 5, wherein the triggering means comprise a coil, by which a magnetic field may be generated, which at least partially, preferably completely compensates for the retention force of the permanent magnet.

7. The lancet device according toclaim 6, wherein the permanent magnet is situated fixed in relation to the coil.

8. The lancet device according toclaim 6, wherein the coil is connected to an internal current source of the lancet device via a current buffer and/or a voltage converter to generate high-performance current pulses.

9. The lancet device according toclaim 6, wherein a coil core is situated in the coil, which is formed by the permanent magnet or contains the permanent magnet.

10. The lancet device according toclaim 9, wherein the permanent magnets enclose a drive chamber, in which a coil core is movable, whose movement is transmitted in operation to the lancet as the piercing and retraction movement.

11. The lancet device according toclaim 10, wherein the permanent magnets are implemented as magnet rings.

12. The lancet device according toclaim 1, wherein the magnetic field generated by the further permanent magnet of the drive means is reinforced by constructive superposition with a further magnetic field, which is generated using a coil current, in a first phase of a piercing movement, in which the lancet is accelerated by the drive force in the direction toward the skin surface.

13. A method for generating a piercing wound in a skin surface using a lancet, in which the lancet is accelerated along a piercing path in the direction toward the skin surface using a drive force generated by a drive spring, wherein the drive spring is held in a tensioned state before the triggering of a piercing movement using a magnetic retention force oriented opposite to the drive force, and the retention force is reduced enough to trigger a piercing movement so that the drive spring relaxes and the lancet is accelerated in the direction toward the skin surface under the effect of the drive force generated by the drive spring.

14. The method according toclaim 14, wherein the magnetic retention force is generated using a permanent magnet and the retention force is at least partially, preferably completely compensated for by a magnetic field generated using a coil to trigger a piercing movement.

15. The method according toclaim 15, wherein a magnetic field, which reinforces the retention force exerted by the permanent magnet, is generated using the coil to support a retraction movement of the lancet.

16. The method according toclaim 15, wherein after a completed piercing, a mechanical oscillation of the drive spring is excited using the coil by periodic current surges, by which a pushrod carrying the lancet returns into its starting position, in which it is held by the retention force of the permanent magnet.

17. The method according toclaim 13, wherein a further permanent magnet is used in the drive means which is situated with opposite polarity to the permanent magnet generating the retention force.

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